Wot, no oil pressure release / relief valve? Square 4 Mk1

[paul.jameson]

To answer Nev's point, I have known of a number of bikes which have combinations of 4G/MkI/MkII cranks. None with such a combination seem to be bad on vibration and it may be that the two best bikes I have ridden from a vibration point of view both had Mk II rear cranks and Mk I front cranks.

To answer Simon's point, all pushrod Squares have the drain from the front timing side main into the crankcase, apart from the very first 4G models. My 4G lacks this drain but is engine no 164, so the 64th produced. It is impossible to prevent an oil leak from the front crank cap once oil pressure hs built up on a long run so I have drilled the crank cap and fitted a drain to that which feeds back into the oil tank. Drilling the drain hole is an option, but a few degrees of error either way will ruin the crankcases so the best way to do this is to strip the engine and drill the hole using a suitable tilting head mill. I don't have the courage to drill the hole with a hand drill, nor the inclination to strip the engine unless I need to - hence the pipe from the crsnk cap.

Before you go drilling the Mk II crank, do get the drawing of the Mk I crank from Roger so that you know what to do.

[simon.holyfield]

Interesting, thanks Paul.

Do they all have that little shield inside as well?

[allan.walker]

Allan, not sure if anyone has mentioned this but the Mk1 has a drain from the front offside main bearing into the crankcase, for the outflow from the prv.

Happy to assist you with pictures and dimensions if necessary.

Hi Simes. Are you referring to the small hole at the bottom of the inside edge of the threaded aperture in the crankcase, where the cap fits?

I've ordered an OPRV assembly from Drags. If you are able, it would be handy to know the depth of the hole I need to drill in the end of the crankshaft. Also, is it the same i.d. all the way to where the seat for the ball is made (beyond which, I assume it is the i.d. of the existing oil gallery - is this correct?)
Any pictures to clarify would be much appreciated.

Allan.

[allan.walker]

......However ,do check before dissembling the motor to be sure the PO hasn't included an oil pressure release somewhere else.

I do wonder about that, John. There's nothing obvious in the timing case and I can't imagine where else you would put one, other than the end of the crankshaft. The PO may have done something, though....that's why I'm still considering fitting an oil pressure gauge and giving the bike a run.
It would be interesting to know exactly what is happening with the oil pressure, before pulling everything apart.

I don't want to take any unnecessary risks, but the bike has run for 1000 miles without the usual OPRV.....Hmmm...

[allan.walker]

To answer Nev's point, I have known of a number of bikes which have combinations of 4G/MkI/MkII cranks. None with such a combination seem to be bad on vibration and it may be that the two best bikes I have ridden from a vibration point of view both had Mk II rear cranks and Mk I front cranks.

That's good to know.

Before you go drilling the Mk II crank, do get the drawing of the Mk I crank from Roger so that you know what to do.

Thanks Paul, but, being a relative newbie on here, where do I contact 'Roger?'

[Gui.dorey]

Allan,

It’s Roger Gwynn who takes care of club memberships. You likely had contact with him when you registered as a member.
Gui

[paul.jameson]

Only the Mk I has the little shield inside. The 4G and Mk II wouldn't have enough oil flow through the drain hole to justify a shield.

[allan.walker]

It’s Roger Gwynn who takes care of club memberships. You likely had contact with him when you registered as a member.
Gui

Thanks Gui,
I've emailed Roger.

[john.whiting]

Highest pressure will be when the oil is cold,just after the motor is started.....I suspect if you let the motor warm up for five minutes ,there will be no further adverse effects......you should never rev a cold motor anyway,as the thick cold oil can overcome a release valve and pressurize a system excessively.......In any case ,before pulling anything down ,Id check the lube system with air pressure from a compressor and regulator ,and see if there is any release operative.Youd probably need a fairly large airflow to overcome other leakages,and maintain pressure.

[allan.walker]

.....In any case, before pulling anything down, Id check the lube system with air pressure from a compressor and regulator and see if there is any release operative. You'd probably need a fairly large airflow to overcome other leakages and maintain pressure.

I'll have to think how this can be done. It seems that the air pressure would need to be applied before a reservoir of oil. If I were to connect the airline to the oil inlet pipe on the junction block, the air would tend to blow the residual oil in the galleries out through the bearings and into the sump, wouldn't it?